Brush-holder assembly



Nov. 7, 1933. H. F. HARTMAN 1,934,359

BRUSH HOLDER AS SEMBLY Filed July 9, 1931 WITNESSES INVENTOR MTWW$ QMATTORNEY Patented Nov. 7, 1933 PATENT orrlcs BRUSH-HOLDER ASSEMBLY HarryF. Hartman, Pittsburgh, Pa., assignor to Westinghouse Electric &Manufacturing Company, a corporation of Pennsylvania Application July 9,1931. Serial No. 549,703

'7 Claims.

My invention relates to brush-holder assemblies and particularly to suchassemblies as have light compression fingers actuated by dualcompression springs. 1

The structural and operating characteristics of brush holders arebecoming of increasing importance ,in the operation of modern motors.The brush holder must occupy a minimum amount of space and, at the sametime, must maintain substantially perfect brush contact with thecommutator cylinder.

As is well known, the wearing surface of ourrent-collecting devicesdevelops considerable roughness in service, and, in use, this roughnessis sufiicient to raise the brush out of contact with thecurrent-collecting device. Such lifting of the brushes is liableto causesparking or other commutation troubles. Not only does this sparkingoccur between the brush and the current-collecting device, but, becauseof the weight of the brush finger and the inertia of the biasingsprings, the finger itself will be separated from the top of the brushand cause sparking between the brush finger andthe brush. This sparkingfrequently results in serious pitting ofthe currentcollecting device andthe brush finger.

I have found that the cadmium-copper alloy contact tip disclosed in myPatent, No. 1,820,699 materially improves the operation and practicallyeliminates pitting of the finger tip. In conjunction with the aluminumalloy finger of said application, the total inertia of the finger ismaterially reduced and the finger is capable of a more rapid follow-upand a consequent reduction of sparking. However, I have found that aspring capable of producing the necessary brush pressure hasconsiderable inertia and is not suificiently rapid in its follow-up tomaintain contact between the brush finger and the brush. To eliminatethis defect, I employ a dual biasing spring in which one of the springelements is of sufiicient strength to provide the major portion ofthenecessary brush pressure, and the other spring element is ofsufiiciently light weight to substantially overcome the troubles due toinertia while still being of sulficient strength to maintain the brushfinger in firm contact with the outer end of the brush. The lighterspring for maintaining contact between the brush finger and the brushmay be of difierent, and, preferably, of less,

length than the main biasing spring.

Other objects and advantages of my improved brush holder will beapparent from the following detailed description, taken in conjunctionwith the accompanying drawing, in which Figure 1 is a sectionalelevation of a. brush holder embodying my invention,

Fig. 2 is a plan view of my improved brush holder, and

Fig. 3 is a brush finger partially in section, showing a modification ofmy invention.

The apparatus disclosed in the drawing comprises a brush box 1 ofsuitable size and shape to accommodate the desired brush 2. A fingermounting or finger support 4, secured to one side of the brush box, isprovided with a reenforced molded shaft. The reenforcement may consistof a central core 7 of steel or other suitable ma.- terial, and themolded material is preferably graphitized micarta.

Journalled on the shaft is a brush contact finger 10, preferably of castaluminum alloy having an enlarged base 11 for engagement with the shaft5 and a finger-like extension 12. The finger-like extension is providedwith a contact tip 14, preferably of cadmium-copper alloy, having ashank '15 embedded in the cast finger. The shank 15 of the copper tippreferably extends substantially throughout the entire length of thefinger 12 and has a tapped opening 16 near the base of the finger fordirect connection with a current-carrying shunt 18 of any desiredconstruction. However, I prefer to use a pig-tail shunt of fine copperconstruction. The shunt 18 is directly connected to the copper shank 15by means of a suitable connection, preferably a screw 20. The directconnection between the pig-tail and the tip eliminates any possibilityof a high-resistance connection because of oxidized aluminum surfaces.The low-resistance character of this contact is further assured bysoldering or otherwise integrally connecting the shunt directly to thescrew and the surface of the finger, as at 22. The soldering alsoprevents the connection from working loose in service much moreeffectively than can be done by the use of lock washers or other lockingdevices.

If the tip shank 15 is totally imbedded in the finger, as shown in Fig.l, the solder composition must be capable of adhesion to the aluminumsurface. However, if the tip shank is brought to the surface, as shownin Fig. 3, it will not be necessary to use an aluminum solder.

The outer extremity of the contact finger 12 is provided with animproved lift which com- 1 5 prises an integral arcuate portion 25extending upwardly and outwardly from the tip of the finger andterminating in a substantially cylindrical end portion 26. The endportion 26 is so shaped that the hand of the operator may firmly 0 graspthe lift and, when so grasped, the end por tion of the lift will form aretaining depression in the operators hand without danger of cutting orabrading the same.

The contact finger is provided, at its base portion, with an angularlyextending portion adapted for contact with a biasing spring. Preferably,the angularly extending portion consists of spaced parallel extensionshaving a spring seat support 31 of suitable material between them. Inthe illustration, the spring seat is a steel pin extending between theextension fingers. A similar spring seat support 33 is provided in thefinger support 4. Between these spring seat supports is mounted myimproved biasing spring.

My biasing spring comprises inner and outer spring members 35 and 36,both connected to spring seats for engagement with the spring seatsupports 31 and 33. The outer spring element 36 is made of comparativelylarge spring wire and is capable of furnishing sufficient energy formaintaining the brush in proper contact with a current-collecting device(not shown).

Preferably, the inner and outer spring elements are wound in differentdirections so that, in operation, there will be no possibility of onespring fouling the other, as would be the case if both springs werewound in the same direction. The inner spring element 35 will be ofsubstantially lighter spring wire and is used primarily for maintainingcontact between the brush finger and the top of the brush.

My dual compression spring is provided with improved spring seats 40 formaintaining the spring elements in proper relation. The spring seat 40comprises a head portion having a groove 42 for engagement with thespring seat supports and an annular portion 43 for engaging the terminusof the outer spring element 35. A substantially cylindrical guideportion 45 within the spring 36 is provided to maintain the spring inproper relation to the spring seat. This guide portion 45 is furtherprovided with an annular portion 48 for engagement with the end of theinner spring 35 and a reduced guide portion 50 extending within theinner spring.

While I have shown and described a specific embodiment of my invention,it is evident that various modifications thereof may be effected withoutdeparting from the spirit and scope of my invention. I desire,therefore, that only such limitations shall be imposed as are indicatedin the appended claims.

I claim as my invention:

1. A brush-holder finger comprising a cast alloy of aluminum body havingan enlarged base and an extending finger, a finger lift extending abovethe end of the finger and having means for providing a firm grip on saidlift, a cadmium-copper tip having its shank imbedded in the finger forsubstantially its entire length, and a flexible shunt connected directlyto the copper shank of the tip near the base of the finger.

2. A brush finger comprising a body portion of cast aluminum alloy, afinger portion extending from said body, a cadmium-copper contact-tiphaving a shank imbedded in said finger, a pigtail connected directly tosaid shank and a spring support angularly disposed in relation to saidfinger portion.

3. A brush-holder assembly comprising a brush guide, a brush fingersupport connected thereto, a brush finger pivotally mounted on saidsupport, said brush finger comprising a body of cast aluminum alloyhaving a finger extending from said body, a contact member having ashank imbedded in said finger, and a spring support in angularlydisposed relation to said finger, a spring seat on said support and aplurality of helical compres sion springs connected to said seat.

4. A brush-finger assembly comprising a cast aluminum alloy fingerhaving an integral enlarged base, a copper tip extending from the end ofsaid finger and having a shank extending substantially the entire lengthof the finger, a dual biasing spring attached to said base for holdingthe finger tip in contact with a brush, a currentcarrying shuntextending to the top of said finger, and a connector extending throughthe shunt and making metallic connection with the tip shank, said shuntbeing soldered to said connector and to said finger.

5. A brush-holder assembly comprising a brush box, a plurality ofparallel plate-like supports for a brush finger brazed to said brushbox, a graphitized molded material shaft secured in said supports, abrush finger journalled on said shaft, a contact tip imbedded in saidfinger, a shunt for supplying current to said finger, means for makingdirect contact between said shunt and said tip, an offset spring supporton said finger and a dual biasing spring for biasing said finger towardsaid brush box.

6. A spring-finger assembly for a brush holder comprising a castaluminum alloy body having an enlarged base and a copper contact tip, acompound helical biasing spring connected to said base, an ofiset springsupport on said base for receiving the end of said spring, a bearing inthe base, a reenforced shaft of graphitized molded material extendingthrough the bearing for supporting said finger.

'7. In combination, a brush box, a finger support on said box, areen'forced graphitized micarta shaft secured on said support, a brushfinger of cast aluminum alloy journalled on said shaft, 2. springsupport on said finger, a spring support on said support and a dualbiasing spring between said supports for biasing said brush fingertoward said brush box.

HARRY F. HARTMAN.

